In Magnetic Resonance Imaging, as well as in every imaging arrangement, image fidelity is described by an imaging technique- and system-specific transfer function, known as Point Spread Function (PSF), which may be defined as the representation of how a single point of real space is mapped in the image space.
An ideal PSF provides a perfect point, whereas any deviation from this ideal state leads to image artifacts such as blurring or ghosting. In order to avoid such problems as much as possible, the PSF shall be maintained as close as possible to the ideal state.
This result is achieved by various methods, which may be basically divided into two general classes: the methods of the first class are intended to act upon the physics of the system, by equalizing the received signals in various manners; conversely, the methods of the second class are intended to act upon k-space filling modes.